Such filter seals are for instance applied in rolling element bearings for use in an oil splash environment, e.g. in a gear box. In order to provide an appropriate lubrication, oil may enter the bearing space through the filter seal, whereby contaminations such as wear particles from the moving components such as tooth gears may be filtered out. An example of such filter seal is shown in GB-A-1319953.
Apart from wear particle contaminations, water contamination is a matter of concern as well. Water contaminant in oil exerts a detrimental effect on bearing life in particular. The negative effects thereof have often been attributed to the mechanism of hydrogen embrittlement.